The appearance of representatives of SA's four big banks before the Zondo Commission of Inquiry into State Capture this week was unprecedented. They had come to give evidence of the pressure they faced when, in 2016, they closed the accounts of various Gupta family members and related entities.

The account closures and the fact that the Guptas' company, Oakbay, lost its both its JSE sponsor and auditors forced the crony family out of the market and marked the beginning of their end.

For several years prior to ending their work with Gupta-linked entities, the banks had reported suspicious activities on various accounts to the Financial Intelligence Centre. This week, the executives outlined how that had come to be.

South Africa has one of the world's top financial systems, as noted by the annual rankings of the World Economic Forum. Our banks are conservative and compliance-heavy and often risk averse. This latter quality often lands them in trouble with the government and radical parties like the South African Communist Party and the EFF, but that conservatism is well-respected in global financial circles.

In addition, when South Africa joined the Financial Action Task Force, the OECD-hosted body that oversees the development of stringent global anti-money laundering laws, the banks created compliance systems which allowed them to follow the money.

They were the first institutions to be able to show that the Guptas were up to no good and their reports to the Financial Intelligence Centre were used by former Finance Minister Pravin Gordhan to push back against growing pressure he faced to get the banks to rescind the decisions to close their accounts.